1. Field of the Invention
The invention relates to a vehicle cruise control apparatus, and more specifically relates to a vehicle cruise control apparatus and a vehicle cruise control method that do not stop an automatic cruise control when brake operation by a driver is detected.
2. Description of the Related Art
In order to lessen the burden on the driver of driving a vehicle, vehicles are equipped with a vehicle cruise control apparatus that performs an automatic cruise control, such as a cruise control which controls the vehicle at a fixed speed so that a vehicle speed is equal to a target vehicle speed, or a tracking cruise control which causes the vehicle to track the preceding vehicle, that is, an adaptive cruise control (ACC). The vehicle cruise control apparatus performs a coordinated control of an engine that provides a driving force to the vehicle and a brake device that provides a braking force to the vehicle in order to make the vehicle speed equal to the target vehicle speed. With the vehicle cruise control apparatus, a target driving force is calculated as a target controlled variable by an automatic cruise control ECU in order to make the vehicle speed equal to the target vehicle speed; the calculated target driving force is output to an engine ECU; and the engine ECU controls the engine, which is a vehicle speed adjusting device that adjusts the vehicle speed, based on the target driving force. Furthermore, with the vehicle cruise control apparatus, the target braking force is calculated as a target controlled variable by the automatic cruise control ECU in order to make the vehicle speed equal to the target vehicle speed; the calculated target braking force is output to the brake ECU; and the brake ECU controls the brake device, which is a vehicle speed adjusting device that adjusts the vehicle speed, based on the target braking force. The vehicle cruise control apparatus according to related technology stops the automatic cruise control when drive operation is performed by the driver.
Related technology has been proposed that does not cause the vehicle cruise control apparatus to stop the automatic cruise control even when brake operation is performed by the driver. For example, technology is proposed in Japanese Patent Application Publication No. 2004-90679 (JP-A-2004-90679) that does not stop the automatic cruise control even when brake operation is performed by the driver. In the technology, the automatic cruise control ECU reduces the target vehicle speed, and calculates the target driving force so that the vehicle speed becomes equal to the reduced target vehicle speed. The engine ECU controls the engine based on the target driving force calculated by the automatic cruise control ECU, thereby reducing the vehicle speed.
There has been demand in recent years to perform the automatic cruise control at a low vehicle speed, for example, at approximately 10 km/h. With a vehicle cruise control apparatus according to related technology, the automatic cruise control is stopped when the driver performs brake operation while the vehicle is moving at a low vehicle speed on a slope under the automatic cruise control. When the automatic cruise control is stopped while the vehicle is moving at a low speed on a slope, there is a possibility that the position of the vehicle may not be maintained, and thus, the behavior of the vehicle may change, for example, the vehicle may roll back down on an upward slope, if the vehicle cannot be maintained in a stopped condition on the slope by the braking force produced by the brake operation performed by the driver.